Method and composition for controlling foaming in oil wells



3 103 634 1 Murnon AND coMPosmoN rou CONTROL- LING FOAMING IN on. WELLSJoseph F. Chitturn, Whittier, Califl, assignor to California "ResearchCorporation, San Francisco, Calif., a corpoyration of Delaware i NoDrawing. Filed July 15, 1960, Scr. No.42,957

, 6 Claims. (Cl. 16641) The present invention relates to improving thepro ductivity of oil wells, and pertains more particularly to improvingproductivity of pumping oil wells which produce petroleum having atendency to foam within the,

well.

.All too often it is found that when a well reaches, the stage j;ofhaving to be produced by pumping, the oil entering the annulus in theborehole surrounding the producing string of tubing from the pump to thesurface tends to form an altogether too stable foam.- When it is desiredto wih-draw gas from the annulus of (the well, the column of foam risessometimes to a height of 5,000 ft. and often .to a height of 1,000 to2,000 ft. in the annulus. Such a column of foam exerts a considerableback pressure on the producingz ones and, hence, tends to reduce theamount of oil which is produced from said zones into the borehole.Further, the formation of foam inthe borehole reduces the accumulationoftheliquid petroleum in the portiono ffthe borehole from which the pumptakes suction. Hence, the pump often takes suction on foam rather thanliquid rpetroleum, thereby greatly reducing the efliciency of the pump.Both these effects result in a decreased oil production of the well.

, Therefore, an object offmy invention is to provide an improved processfor increasing the productivity of oil wells in which the oil tends tofoam. A further object is to provide a method or con-trolling foaming inan oil well in a mannerthat requires less foam inhibitor than heretoforeconsideredpractical. Another object of my invention is to provide an{improved foam inhibitor stick composition which is especially suitedfor use in controlling excessive foaming of oil in pumping wells. .Withthe above objects 1in mind, I have found that the productivity of theWell can be appreciably increased by controlling the foam illth annuluswhile pumping the well and withdrawingygasfrom the annulus asdelsired; lhave further found that oil well foamsare generally of two differenttypes. One widely occurring type, is that which has apositive charge onthe inner surface of the. electrical double layer of {the foam bubble.Such positively-charged foams can be controlled and the producftivity ofthe well maintained at arelatively high level by a simple procedure ofproperly placing within the annulus of a well my new foam-inhibitingcomposition. By

. the use of the present .invention, excessive amounts of suchpositively-charged foams in an oil well. can be avoided in aconvenientma nner without muchinterference with normal operations andwith less foam inhibitor than heretofore considered practical.

Heretofore it has been proposed to suppress foaming by the use ofsiliconefoam inhibitors in oil solutions. Greatly diluted solutions ofsilicones have been tried in both the laboratory and t he field, butwithout practical success. If, for instance, a dilute kerosene solutionof silicone is introducedinto the well annulus, itprobably flows downthe casing or tubing with channels or fingers 3,108,634 Patented Oct.29, 1963 "ice surface of the foam without being erratically held upalong the length of the casing and producing string. Intrinsic in such amethod are the difficulties of fingering and waste of chemical bydiversion into ineffective areas.

In contrast to the above, the present method efficiently reducespositively-charged foams with a minimum consumption of expensivechemicals. While I do not wish to be bound by theory, the success of mymethod appears to result from fulfilling several criteriasimultaneously. Thus, the foam inhibitor is specifically compounded withanionic sulfonates to break up positively-charged foams. Further, theinhibitor is quite concentrated at its point of action. That which getsinto the bulk of the foam is that naturally carried downward by thebreaking foam. Consequently, the rate of use of the concentratedinhibitor is very low. Also, the inhibitor tends to disperse over thewhole surface of the foam after contact, and hence, fingering isminimized. Moreover, these efficient conditions are set up more or lessautomatically by the nature of the process. These advantages and objectsfollow from the practice of the invention, as described hereinafter.

To determine whether the foam in the well annulus is positively charged,and hence, susceptible to treatment by the present invention, anysuitable method can be used to test the charge on the inner layer of thefoam bubbles. One test uses an H-shaped electrophoretic cell and thetest oil is placed in both legs of the cell. Foam is generated bybubbling gas through the oil until a steady state withpressure-temperature equilibrium is reached. Then a medium high fieldstrength is placed across the cell by applying a DC. current to theelectrodes placed in the cell legs. If the bubbles are positivelycharged, they will move toward the negative electrode. This movement canbe detected easily by viewing the bubbles through a microscope trainedat the cross channel of the H-cell.

Another procedure is to make foams in two test tubes with the oil fromthe well. This can be done by placing in each tube 10ml. of the test oilplus 5 ml. of distilled water. The water is boiled until several inchesof foam are produced. Then to one tube of foam is added 0.25

g. of an oil-soluble alkali, metal sulfonate such as the sodium salt ofmahogany sulfonic acid of about 450 molecular weight. To another foamsample is added a similar amount of the imidazoline of ricinoleic acid.If the foam is more rapidly broken with the sulfonate, the foam ispositively charged. If it is more rapidly broken with the imidazoline,the foam is negatively charged.

As a first step in the process of the present invention, the column offoam in the annulus of the well is substantially depressed to areasonable level. One suitable method consists of temporarilydiscontinuing the withdrawal of gas from the annulus of the well,whereby the pressure within the well is allowed to build up and thecolumn of foam reduced. Other means of obtaining the initial reduotionof the foam column can also be used, such as by injecting into theannulus a large slug of liquid foam inhibitor.

After the positively-charged foam column is initially depressed, amixture of particular proportions of certain sulfonates and silicones,as described later, are added at or near the upper surface of the foamcolumn. This is done most efliciently as well as most conveniently bydropping my preferred new foam inhibitor stick into the annulus so thatit comes to rest at a point above the producing zone and near, butspaced above, the top of the depressed column of foam. If a tubinganchor is not positioned within the annulus so that the foam inhibitorsticks are properly placed, then a suitable catcher or porous barrier ofsome kind is placed in the well to cause the foam inhibitor sticks tocome to rest in the desired position.

The composition of the foam inhibiting sticks is such that they. slowlymelt and/ or are leached with condensate of petroleum vapors. In thisway foam inhibitor in relatively high concentration is continually addedto the top portion of the foaming liquid in sufficient amount to controlthe foaming tendency. Thus, hydrocarbon condensate on the inhibitorsticks dissolves silicone and sulfonate. The drops of condensate becomeconcentrated solutions of silicone plus sulfonate by the time they fallon to the foam surface. The sulfonate surfactant aids in dispersing theagents rapidly over the foam surface. In this way a high siliconeconcentration is mainly in the surface layer of foam only. Thisconcentration on the surface is desirably about 100 ppm. and may be300-400 ppm. of the oil, but in the layers below the foam surface thesilicone concentration may be 5-15 p.p.m. or less. Since the foamcontains only a relatively small amount of oil, the total siliconerequirement is extremely low, For example, where the foam height isdepressed from 4,000 ft. down, and stabilized at, 500 feet and oilproduction is 150-200 barrels per day, the silicone required is probablyless than 0.1 ppm. of the total oil produced.

After the foaming is brought under control, the withdrawal of gas fromthe annulus at the top of the well may -be re-established. The supply offoam inhibitor sticks in position in the well annulus is maintained byintroducing additional sticks from time to time.

By the present invention foaming is controlled and the productivity ofthe well can be increased substantially. For example, in an extremeinstance of high foaming tendency in a well where a column of foam roseto 5,000 ft. in the annulus, it was found that the productivity of thewell could be increased by about 50% to 100% by means of theabove-described treatment of the present invention.

Preferably, my foam-inhibiting sticks consist essentially of threeingredients. The first ingredient is a petroleum wax having a meltingpoint in the range of 150 to 200 F. which is satisfactory for use inwells of relatively normal temperatures. Higher melting point waxes areused where extremely high temperatures are encountered. Preferably themelting point of the wax is sufliciently high to provide a stickcomposition having a melting point ranging from 525 F. above thetemperature of the liquid petroleum produced into the borehole.So-called micro-crystalline waxes are preferred because they combine thedesirable properties of relatively high helting point and compatibilitywith the other ingredients. The wax normally comprises 50 to 80% of thefoam-inhibiting stick composition. The remainder of the foam inhibitingstick composition is a mixture consisting of to 90%, preferably to 80%,of dimethyl silicone polymer having a viscosity in the range of 500 to100,000 centistokes, the remainder of said mixture being apreferentially oil-soluble alkali metal sulfonate such as sodiummahogany sulfonate, potassium mahogany sulfonate, and like anionsurface-active salts of various oil-soluble alkylated aromatic ornaphthenic sulfonic acids. Preferably the dimethyl silicone polymer hasa viscosity in the range of 25,000 to 75,000 centistokes. The sulfonatescan be obtained by neutralizing the sulfonic acids such as mahoganysulfonic acids having molecular weights of 400 to 500 which arerecovered in the sulfuric acid treatment of lubricating oil stocks.

The effect of the desired ratios of silicone and sulfonate a an oil wellis shown in the following graph:

in diameter and a length EFFECTIVENESS OF SULFONATE-SILICGNE MIX- TURESTO INHIBIT POSITIVELY-CHARGED FOAMS Percentages of Ingredients 7(Sulfonate-upper number; Silic0ne1ower number) These results wereobtained from tests run with a crude oil giving a positively-chargedfoam and. having a high foaming tendency as observed from a 5,000-footfoam column in the well producing the oil. In the test, a vertical tube12 inches high with an internal diameter of 0.95 inch was used. Thecrude oil was poured into the tube to a height of 2 inches. Foam wasproduced up to the IO-inch level by dispersing nitrogen gas in the oil.Then a rod with the inhibitor material on the end was lowered into thesurface of the foam. The effect of each material after one minute wasnoted, and the percentage of the original foam height was determined.The graph shows these precentages for various proportions ofpolymethylsiloxane of about 30,000 centistoke viscosity and sodiummahogany sulfonate of about 475 molecular weight. The graph shows thatin the test either 100% silicone or 100% sulfonate increased the foamheight, but that silicone-sulfonate mixtures, especially mixtures of2080% silicone plus sulfonate as the remainder, gave effectivereductions in foam.

In another series of tests, polymethylsiloxanes of different viscositieswere substituted for that used above. Those with viscosities of 12,500and 60,000 centistokes were as effective as the silicone of 30,000centistoke viscosity, while a silicone of 1,000 centistoke viscosity wasabout as effective.

The over-all composition of the foam-inhibiting sticks is adjusted wherepossible to provide a melting point for the composition of about 5 to 25F. above the tempera ture of the liquid oil accumulated at the bottom ofthe well. For example, a foam-inhibiting stick which is formed as acylinder weighing about one-half pound and has a melting point of about180 F., when placed in position in a well having a bottom hole liquidtemperature of 170 R, will have a life of about hours.

The foam inhibitor composition above described may be formed into shapessuitable for introduction into the annulus of a well and easy placementin position above the top of the depressed foam column in the well. Onedesirable shape is a relatively thin cylinder of about onehalf orthree-quarters of an inch up to one or two inches of five to twentyinches. A convenient size is a stick of one inch diameter by twelveinches long which for a composition" of 15% dimethyl riod.

t at about this temperature.

tions of the present invention can 'be made. centages given herein arepercentages by weight, except silicone polymer of 30,000 centistokesviscosity, 15% sodium mahogany sulfonate derived from a mahoganysulfonic acid of 450 molecular weight, and 70% of a petroleum paraffinwax having a melting point of 190 to 195 i F., weighs about one-halfpound. Although the number of such sticks that will be used dependsprimarily on the particular foaming tendency of the petroleum beingproduced, it has been found that for a particularly severelyfoaming wellthe initial treatment may comprise 25 to 30 sticks of the aforesaidcomposition with the addition of 6 to 10 sticks twice a week to maintainthe foaming tendency under control.

While the above'described stick composition is the preferred means ofcontrolling positively-charged foams in oil wells, the invention alsocontemplates injecting into the top of depressed column of such foam themixture of 10jyto 90% dimethyl siliconepolymer with 500 to 100,000centistoke viscosity and the remainder a preferentially oil-solublealkali metal sulfonate as an anionic surfactant.

The mixture can be injected at the proper level in the well annulus byany suitable means such as a small reservoir fitted with a drip valve ora string of small tubing from the well surface.

1 The following examples are given to further illustrate the presentinvention.

- Example 1 Solid foam sticks one inch in diameter and 14 inches inlength were prepared witha composition of 50% of polymethyl siliconematerial of about 60,000 centistoke viscosity, 25% of a microcrystallinewax with a melting point of about 150 F. and 25% sodium mahoganysulfonate of molecular weight of about 475. The sticks were prepared bymelting the wax, adding the other ingredients and stirring until themixture was homogeneous. Then this melted mixture was poured intocardboard tubes and allowed to cool. Thesticks had a melting point ofabout 145 F. t

i 1 Example 2 i the test well a 4,900-foot column of foam stood in theannulus between the casing and tubing. Before the test the well wasproducing at about 120 barrels of crude oil per day. Then the stocksprepared in Example 1 were dropped into the casing of the well, whichcontained a tubing anchor about 500 feet above the producing zone. Tensticks were dropped into the well the first day, six each the second andthird day, ten the fourth day, and twenty the fifth day. The productionfrom the well increased by about 50 barrels per day after a five-day pe-Example 3 Sticks of about the same shape as those in Example 1 but of ahigher melting point by containing 70 parts of a petroleum paraffin waxof 190/195 F. melting point, 15 parts polymethylsil-oxane of 60,000centistoke viscosity and 15 parts of sodium mahogany sulfonate of about450 molecular weight. These sticks have a life span in a hydrocarboncondensate atmosphere at 170 F. of about 110 hours. 'I hus, they,wouldlast for a long time and slowly give up concentrated inhibitor ina normal well Obviously, modifications-some less desirable thanothers-of the above examples of the method and composi- All perwherespecifically indicated to be otherwise.

I claim:

1. In a method of operating a pumping oil well in which the oil tends tofoam within the well and wherein oil is produced by a pump near thebottom of the well a up through a producing string of tubing, gas iswithdrawn from the annulus of the well outside of the producing string,and a positively-charged foam tends to accumulate in the annulus therebygenerating a back pressure on the producing Zones and tending to reducethe efficiency of said pump, the improvement of increasing theproductivity of said oil well which comprises the steps of temporarilydiscontinuing said removal of gas from the annulus of the oil well tocause the column of said foam in the annulus to be substantiallydepressed, then positioning in said annulus near but spaced above thetop of the depressed column of foam standing in the annulus of the wella solid foam-inhibiting composition consisting essentially of 5080% waxhaving a melting point above 150 F. and the remainder consisting of atleast 10% each of dimethyl silicone polymer having a viscosity of 500 to100,000 centistokes and preferentially oil-soluble alkali metalsulfonate, said solid inhibiting composition having a melting point offrom 5 to 25 above the temperature of the well at the point therein inwhich the said composition is placed, thereafter re-establishing thewithdrawal of gas from the annulus of the well and maintaining withinsaid annulus a sufficient quantity of said solid foaminhibitingcomposition to keep the column of foam depressed below the point atwhich said foaminhibiting composition is placed in said annulus.

2. In a method of operating a pumping oil well in which the oil tends tofoam within the well and wherein oil is produced by a pump near thebottom of the well up through a producing string of tubing, gas iswithdrawn from the annulus of the well outside of the producing string,and a positively-charged foam tends to accumulate in the annulus,thereby generating a back pressure on the producing zones and tending toreduce the efficiency of said pump, the improvement of increasing theproductivity of said oil well which comprises the steps of initiallydepressing substantially the column of said foam in the well annulus,and then maintaining said foam column depressed by adding to the top ofthe depressed foam column a mixture consisting essentially of at least10% each of dimethyl silicone polymer having a viscosity of 500 to100,000 centistokes and preferentially oil-soluble alkali metalsulfonate.

3. In a method of operating a pumping oil well in which the oil tends tofoam in the well and wherein oil is produced by a pump in the bottom ofthe well up through a producing string of tubing, gases are withdrawnfrom the annulus of the well outside of the producing string and apositively-charged foam tends to accumulate in such annulus, therebygenerating a back pressure on the producing zones and tending to reducethe efficiency of said pump, the improvement of offsetting the tendencyof said foam to accumulate and of increasing thereby the productivity ofsaid oil well by adding to the top of the column of foam in said annulus,a mixture consisting essentially of at least 20% each of dimethylsilicone polymer having a viscosity of 500 to 100,000 centistokes andpreferentially oil-soluble alkali metal sulfonate.

4. An improved foam inhibitor stick composition adapted to controlfoaming in the annulus of oil wells, said composition consistingessentially of 50 to by weight of a petroleum wax having a melting pointin the range of to 200 F. and the remainder consisting essentially of amixture of at least 20% each of dimethyl silicone polymer having aviscosity of 500 to 100,000 centistokes and preferentially oil-solublealkali metal sulfonate.

5. The composition of claim 4, wherein said composition is cast intoelongated shapes adapted for insertion into the annulus of oil wells.

6. The composition of claim 4, wherein said wax is a microcrystallinewax.

References Cited in the file of this patent UNITED STATES PATENTS2,453,352 Tremain et al. Nov. 9, 1948 2,585,522 Watts et al. Feb. 12,1952 2,698,295 Cardwell et al. Dec. 28, 1954 2,993,223 Krammes July 25,1961 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.108,634 October 29, 1963 Joseph F. Chittum It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 3, line 25, for "about" read above line 58, for "helting" readmelting Signed and sealed this 28th day of April 1964.

(SEAL) Altest:

ERNEST W SVIDER EDWARD J. BRENNER Attestmg Officer Commissioner ofPatents

3. IN A METHOD OF OPERATING A PUMPTING OIL WELL IN WHICH THE OIL TENDSTO FOAM IN THE WELL AND WHEREIN OIL IS PRODUCED BY A PUMP IN THE BOTTOMOF THE WELL UP THROUGH A PRODUCING STRING OF TUBING, GASES ARE WITHDRAWNFROM THE ANNULUS OF THE WELL OUTSIDE OF THE PRODUCING STRING AND APOSITIVELY-CHARGED FOAM TENDS TO ACCUMULATE IN SUCH ANNULUS, THEREBYGENERATING A BACK PRESSURE ON THE PRODUCING ZONES AND TENDING TO REDUCETHE EFFICIENCY OF SAID PUMP, THE IMPROVEMENT OF OFFSETTING THE TENDENCYOF SAID FOAM TO ACCUMULATE AND OF INCREASING THERBY THE PRODUCTIVITY OFSAID OIL WELL BY ADDING TO THE TOP OF THE COLUMN OF FOAM IN SAID ANNULUSA MIXTURE CONSISTING ESSENTIALLY OF AT LEAST 20% EACH OF DIMETHYLSILICONE POLYMER HAVING A VISCOSITY OF 500 TO 100,000 CENTISTOKES ANDPREFERENTIALLY OIL-SOLUBLE ALKALI METAL SULFONATE.